[Refactor Xcode Objects] Decouple file references and indexing target.

Previously, whenever a file reference needs to be added for indexing, a default
target with the same name as the project is always assumed to be the one to
bound to.

This CL decouples file references from the default indexing target, and allows
file references to be bound to any of the native targets.

BUG=614818

Review-Url: https://codereview.chromium.org/2577753002
Cr-Original-Commit-Position: refs/heads/master@{#439894}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: 898a56b7966c5686d276b6aa7f27ec922b37ab38
3 files changed
tree: 5169ec1f6aa060501f43c85d50fc308046a95863
  1. tools/